In the HPLC, a sample to be analyzed must be fed into a high-pressure liquid flow; meanwhile, any interruption of this flow must be as short as possible. For this purpose, high-pressure injection valves are used that enable a nearly uninterrupted switching of the liquid flow. Such an arrangement is described, for example, in the U.S. patent specification U.S. Pat. No. 3,530,721 A.
The injection valves currently being used have at least four ports to be able to conduct a sample pre-compression by means of a sample conveying system. An additional port is needed when the solvent contained in the sample conveying system or a sample taken incorrectly is to be discarded through a waste port that is connected to the injection valve. A sampler with a corresponding injection valve is already described in DE 10 2008 006 266 A1.
When the solvent is changed in an HPLC system, it is necessary to flush out old solvent in the lines between the solvent bottles and the injection valve, likewise through the waste port. There is the possibility here, for example, to run the so-called injection needle directly over a waste tank and dispose the content of the line by means of the solvent pump. The disposal is generally referred to as a “purge.” The previously mentioned change of solvent is described, for example, in U.S. Pat. No. 6,129,840 A.
Furthermore, with most of the injection valves in the state of the art, some connecting lines of a sampler are not completely flushed in the so-called injection position (INJECT position), meaning the position during which the sample is applied on the chromatography column. The connections that are embodied most frequently in the form of grooves in the stator or rotor of the injection valve are required to enable switching back and forth between the so-called load position (LOAD position; adding the sample to a sample loop of the injection valve) and the pressure compensation position (PRESSURE COMPENSATION position; position in which the sample loop is brought to system pressure or ambient pressure), yet also to enable switching back and forth between the LOAD position and the PRESSURE COMPENSATION position, without interrupting the solvent flow to the column. The flow must not be interrupted for the reason as the pump pressure would rise otherwise and the column pressure would drop enormously. The former is problematic for reasons of safety and the latter requires long equilibration phases between the sample analyses. The solvent that was used in the beginning of the chromatography run (e.g. in the equilibration phase) collects in the mentioned grooves and falsifies the gradient composition in the further course by mixing the solvent residue with the gradient (particularly critical in low-flow/nanoflow applications).
The problem to be solved by the present invention is therefore the provision of an injection valve with relatively simple arrangement to be used in a sampler for liquid chromatography applications, which can work with the fewest ports possible and the fewest grooves connecting the ports, while having a high density and no areas that are not flushed, and which can furthermore be produced at low cost, while the valve enables a pre-compression without an interruption of the solvent flow from the pump to the column arising in the transition from the LOAD position to the PRESSURE COMPENSATION position. Another problem to be solved is to provide an injection valve in which all grooves of the valve are flushed through completely in the INJECT position.